Amorphous Silicon Films and Superlattices Grown by Molecular Beam Epitaxy: An Optical Analysis
- PDF / 126,771 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 20 Downloads / 268 Views
AMORPHOUS SILICON FILMS AND SUPERLATTICES GROWN BY MOLECULAR BEAM EPITAXY: AN OPTICAL ANALYSIS D. J. LOCKWOOD1, J.-M. BARIBEAU1, M. NOËL2, J. C. ZWINKELS2, B. J. FOGAL3, F. ORAPUNT3, and S. K. O'LEARY3 1 Institute for Microstructural Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6 2 Institute for National Measurement Standards, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6 3 Faculty of Engineering, University of Regina, Regina, Saskatchewan, Canada S4S 0A2 ABSTRACT We produce a novel form of amorphous silicon through ultra-high-vacuum molecular beam epitaxy. By depositing silicon atoms onto a fused quartz substrate at temperatures between 98 and 335 oC, we obtain a silicon-based material that lacks the characteristic periodicity of crystalline silicon but nevertheless has 98% of its density. The impurity content of this material is studied through infrared and secondary ion mass spectroscopies. The primary impurity found is oxygen, with hydrogen and carbon atoms also being found at trace levels. The Raman spectra of the amorphous silicon films are measured and the results, as they relate to the presence of disorder, are interpreted. We also use this molecular beam epitaxy method to fabricate a number of amorphous silicon superlattices, comprised of thin layers of amorphous silicon separated with even thinner layers of SiO2. The optical properties of the films and superlattices are contrasted. INTRODUCTION Owing to its remarkable potential for electron device applications, amorphous silicon (a-Si) remains a focus of intensive investigation. Typically, device-quality a-Si is fabricated through the plasma decomposition of silane gas [1]. This deposition technique involves the generation of radicals through the dissociation of silane, followed by radical diffusion and reaction processes with the growth surface. The resultant material, a mixture of silicon and hydrogen atoms, may be referred to as plasma-deposited amorphous silicon (PD-a-Si). Research suggests that the hydrogen atoms that reside within PD-a-Si are responsible for many of the favorable electronic characteristics exhibited by this material, these hydrogen atoms passivating the dangling bonds which populate all forms of a-Si [2]. Unfortunately, the electronic properties of PD-a-Si deteriorate when exposed to light [3]. This reversible instability, known as the Staebler-Wronski effect, is also believed to be related to the presence of hydrogen atoms within this material [4]. Accordingly, there has been a considerable amount of effort invested into the development of alternate forms of a-Si that retain the favorable electronic characteristics of PD-a-Si without this instability. Various alternate deposition techniques have been attempted over the years [5,6,7]. In recent years, for example, researchers have deposited a-Si using hot-wire chemical vapor deposition [8,9]. The resultant material was found to be quite stable when contrasted with PD-a-Si. Recently, we have deposited a-Si using ultra-high-vacuum
Data Loading...
